Brakes gone spongy (getting really tense now)

Ok calipers amended (wonders will never cease why someone would spend so much money on getting the wrong parts) now the brakes are spongy ! bled the system down and no fluid is leaking around the pistons.

Is there a technique to bleeding Volvo ABS systems I might not know about. If the ABS System is defective I'm right in thinking the brakes will go heavy like no servo assistance (correct if wrong)

Wondering if there is an airlock somewhere in the system.

I know the replacement calipers are working because the front wheels are getting hot and they aren't nipping as the wheel rotates freely when lifted. Oh there is a bleed nipple on the master cylinder found it whilst checking something else (I don't think this is a stock item)


Advice please.

[Citizen.Agfa]

Hi. No expert but received wisdom is that ABS can be a bugger to bleed effectively; the advice on here has generally been use a powered bleeding system and keep trying.

Sorry I can't be any more help than that, regards, Nick H.

[bb54]

on the 850's you start with the nipple furthest from the reservoir, 3rd, 2nd, nearest.

faulty abs wont make it heavy or spongy, its a sytem for reducing pressure to a caliper/s.

spongy can only be (asuming alls been assembled correctly) ,air in system if spongy when system is cold or hydrated brake fluid if spongy when system is hot.

have you renewed your fluid with a bottle that wasnt new/left open ?
this could cause hydration of the fluid and when it gets hot, boils the water and causes steam/air pockets.
wayne

[TheJoyOfSix]

Originally Posted by charlotte001

Is there a technique to bleeding Volvo ABS systems I might not know about.

Bleeding the ABS is quite easy, do the rears first, doesn't matter which caliper first, then the fronts, again it doesn't matter which side you do first.

Originally Posted by charlotte001

Oh there is a bleed nipple on the master cylinder found it whilst checking something else (I don't think this is a stock item)

The Volvo master cyls do have bleed nipples on them.

Yes it's a brand new bottle of Dot 4 Synthetic fluid. My feeling is there is an air lock somewhere in the system. I did notice, before it got dark that one of the flexi hoses on the front is expanding just fractionally. Tomorrow I'm going to boot some 5.1 through it and drain the entire system by gravity the re-fill and bleed

Also as the calipers are used would the seals take time to re-adjust to being used ? (forgive this as I've never used used calipers before)

Charlotte

[bb54]

Originally Posted by charlotte001

Yes it's a brand new bottle of Dot 4 Synthetic fluid. My feeling is there is an air lock somewhere in the system. I did notice, before it got dark that one of the flexi hoses on the front is expanding just fractionally. Tomorrow I'm going to boot some 5.1 through it and drain the entire system by gravity the re-fill and bleed

Also as the calipers are used would the seals take time to re-adjust to being used ? (forgive this as I've never used used calipers before)

Charlotte

dont think so.

if one flexi hose is swelling, they may all be in a similar state.
id change at least the one hose before continuing.

easy bleed kits are only a £10, they do the job quicker and better.

wayne

On the off chance some things you haven't thought of, I'll "state the bleeding (no pun intended!) obvious" and say:

- take the handbrake off first
- make sure you pump the pedal to push any air out of the master cylinder before starting
- use pressure bleeder in correct sequence and don't pump the brake pedal between each brake
- could try pushing down on the pedal as well while pressure bleeder connected
- make sure the master cylinder is higher up than everything else (not really a problem unless you are parked on a very steep hill!)
- could try removing caliper and angling so bleed screw at the highest point, since the air should rise to the top i.e where the bleed screw is

I don't think you should have any problems with bleeding the ABS I think they bleed themselves.

But what you ought to do is to bleed it, and then go out and make sure you get the ABS to kick in. Then maybe bleed again. Then at least you've got the ABS to pump fluid through.

Of course, you could have a leak letting more air in.

Anything else like extra flexible hoses, well I can't see how they have an affect on trapping the air although obviously they could make the brakes feel like they need more of a shove.

Pete

All done it turned out that one of the dual pistons had siezed.

Charlotte

[turboboy]

Keep the handbrake on (for safety).

On the 740/760 the hand brake is a totally seperate mechanical system working on rear drums, while the hydraulic (footbrake) system is disks all round.

Yes, sorry, you're quite right of course... my list came from my own experience and S40 has handbrake operating on the rear calipers.

And I always leave in gear and chock whatever wheels aren't up in air BTW!

Pete